The present invention relates to a film capacitor or, more particularly, to a capacitor in which the dielectric film material is formed of a unique organosilicon compound having excellent dielectric properties, e.g., a large dielectric constant and relatively low dielectric loss, low moisture absorption, excellent mechanical properties as a film and stability even at an elevated temperature.
It is an outstanding trend in the electronic industry in recent years that various instruments and equipments are required to be compactly designed with a decreased weight and accordingly various electronic components and parts are also requireed to be small in size and light in weight. Capacitors and other electronic devices in which highly dielectric materials play an important role do not make an exception. One of the key factors in order to satisfy this requirement in film capacitors, as a class of capacitors manufactured using dielectric films, is to use a film of a dielectric polymer having a greatly increased dielectric constant and other dielectric properties without affecting other important parameters as a constituent of film capacitors such as moisture absorption, mechanical strengths and thermal stability.
Examples of polymeric materials conventionally used as a dielectric film include cyanoethylated polysaccharides such as cyanoethyl cellulose, cyanoethyl starch, cyanoethyl pullulan and the like, cyanoethylated products of polysaccharide derivatives such as cyanoethyl hydroxyethyl cellulose, cyanoethyl glycerol pullulan and the like, cyanoethylated polyol compounds such as cyanoethylated polyvinyl alcohol and the like, fluorocarbon resins such as poly(vinylidene fluoride) and so on.
These conventional polymeric materials, however, have several disadvantages as a dielectric film material and not quite satisfactory in the electric and electronic applications. For example, the cyanoethylated products of polysaccharides, polysaccharide derivatives and polyvinyl alcohol above mentioned have a defect in common that the moisture absorption thereby is so large that the dielectric properties thereof are subject to a great decrease in a humid atmosphere and the reliability of the electric and electronic instruments constructed by using, for example, film capacitors prepared with the polymer is greatly affected. This problem of course can be solved to some extent by undertaking some measures of humidity control and removal of absorbed moisture in the manufacturing process of film capacitors although the productivity of the process is unavoidably decreased so much even by setting aside the problem that no complete solution of the problem can be obtained at any rate.
In addition, cyanoethyl cellulose and cyanoethyl starch have a problem as a film-forming polymer so that satisfactory polymeric films of these polymers can be prepared only with a great difficulty. Further, cyanoethylated hydroxyethyl cellulose, cyanoethylated glycerol pullulan and cyanoethylated polyvinyl alcohol are defective in respect of the large temperature dependency of the dielectric constant.
Fluorocarbon resins such as poly(vinylidene fluoride) are not advantageous as a material of dielectric films in film capacitors because of their small dielectic constant which is only about a half of that of the above described cyanoethylated polymers although they have advantages in the small moisture absorption and small temperature dependency of the dielectric constant.